Electric discharge system



July 9,1940. R. M. -soMERS ELCTRIC'DISCHAR/GE SYSTEM 2 sheets-sneetl Filed Feb. 6. 1936 July 9# M401 R. M. soMERs 2,207,275

ELECTRIC DISCHARGE SYSTEM Filed Feb.`6, 1936 2 Sheets-Sheet 2 INVENTOR A TORNEY Patented July 9, .i946

UNITED STATES aciers PATENT OFFICE 2,207,215 ELECTRIC DISCHARGE -sYs'rnM Application February s, 193s, serial No. 62,583

17 Claims. (Cl. 17e-122) This invention relates to electric discharge systems, andmore particularly to systems wherein a main arc discharge is maintained between appropriate electrodes in a gaseous atmosphere. Throughout the specification the term gaseous" has been employed as an adjective to denote either a gas or a vapor or a combination of gases and/or vapors, while the terms gas and vapor have each been used in a more specic sense.

It is an object of my invention to providegenerally improved means and methods for starting the main arc discharge.

It is an object to provide starting means and methods adapted to cause the main arc establishment quickly after the supply of current to the system, but with the electrodes in proper condition of emissivity.

It is another object to provide starting means and methods elciently operative. with supply voltages of 110 volts and less, to start the main arc discharge in devices havingmaterial positive columns.

It is another object to provide improved means and methods for quick heating of the electrodes preliminary to the establishment of the arc discharge.

It is another object to provide improved means and methods for automatically reducing such heating upon such discharge establishment.

Other objects lare the provision of a generally improved discharge system and device, and of improved electrode structuresand electrodes therefor.

Other and allied objects will more fully appear from the following description and the appended claims. l

In the description reference is had to the accompanying drawings, of whichf Figure l is a view of a system incorporating my invention, being a partly elevationaland partly vertical sectional view of a typical discharge de' vice together with a schematic diagram of further or circuit portions of the system:

Figure la is an enlarged sectional view of one ofthe electrode structures of the device of Figure 1;

Figure 2 is a view similar to Figure 1 but illustrating a modication of my invention, particularly in respect of the circuit portion of the system;

Figure 3 is an end view of the electrode structure shown in Figure la;

Figures 4 and 4a comprise respectively sectional and end views of the main electrode of the mentioned structure; Y

Figure 5 is a View similar to Figure 1 but ill trating a further modification of my invention;

and

Figure 5a is an enlarged sectional view of one of the electrode structures of the device of Figure 5.

In Figure l I have illustratedan embodiment of my invention which I have ordinarily preferred 10 to employ. The starting circuit arrangement in itself is one known in the art; it has been shown, for example, in the United States Patents Nos. 1,897,642 and 1,980,534 to Pirani et al. and Kirsten, respectively. The starting circuit arrangement l5 comprises auxiliary electrodes respectively adjacent the main electrodes of the discharge device, the auxiliary electrodes being connected together through impedance which may comprise a single resistance elementy or resistor. As employed in 20 the patents abovementioned, the circuit operates to produce ionization, and therethrough to start the main discharge, by the creation of an auxiliary glow discharge between each auxiliary' electrode and the respectively adjacent main elec- 26 trode. There must of course be available sumcient voltage across each auxiliary discharge path to start a glow discharge thereacross in the first instance; and, these paths being mutually in series in the circuit under consideration, it is 80 readily appreciated that the voltage available for starting purposes, whether or notl later required for normal discharge maintenance, is high. According to my invention, however, I may employ across the system, at the-time of starting as well 35 as later, a muchlower voltagefor example, a voltage materially less `than the cold-electrode glow ignition voltage of the two serially connected paths and even less than that voltage of a singleA one such path.' I. preferably provide the auxiliary 40 electrodes with emissive coatings and I substantially heat them, as well as the main electrodes, by appropriate externally energized means; accordingly there may be no glow when current is first applied to the system but, as the cathode fall of both auxiliary and main electrodes is reducing in response to their heating, a discharge between each auxiliary electrode and the respectively adjacent main electrode initiated and rapidly increased, quickly forming astrong auxiliary arc rather than glow discharge. In response to this auxiliary arc discharge the main discharge strikes through the device from one main electrode to the other.v

Reference being had to Figure l, there will be 55 seen the discharge device I, which may for example be a luminous, U-shaped device comprising the elongated glass envelope 2 having the seals 2b and I02b at its respective extremities. The space 2' within the envelope 2 is evacuated of air and filled with a noble gas, such as neon, krypton or argon, or combination of gases. Additionally to the gas filling there may be provided within the space 2' a source of metal vapor, such as the deposit 2" of mercury, adapted to vaporize to an extent depending upon the heating of the device; the source 2" may be quantitatively in excess of the Aamount which can vaporize in the normal operation of the device, in which case the operating vapor pressure will be determined among other things by the cooling facilities of the device. or the source 2" may be quantitatively limited to an amount which will always fully vaporize in normal operation to provide a predetermined vapor pressure. I may mention by way of example that I have employed my invention to great advantage in connection with a device having a quantitatively limited source 2" of mercury vapor adapted to provide an operating vapor pressure of about 10 mm. Hg., and a noble gas filling of argon at a pressure of about 4 mm. Hg.

Passing through the seal `2b are the lead-ln wires 4', 4" and 4"', and through the seal I02b the lead-in wires |04', |04"` and |04"'. On each of these two groups of lead-in wires is supported an electrode structure which is desirably of the furnace type which I have disclosed and claimed in my co-pending application Serial No. 30,798, filed July 11, 1935 (on which Patent No. 2,112,718 has since been issued). 'I'his structure involves relatively low masses, so that the time period required for its heating is inherently short. Since \the two structures, which are identified in Figure 1 as 4 and |04 respectively, are entirely similar, a description of the structure 4 only will be given, it being understood that the structure |04 may comprise an identical arrangement of identical components (to each of which has been assigned a number higher than to the corresponding component of the structure 4). The structure 4 appears in detail in the enlarged cross-sectional Figure 1a.

In the structure 4 the main electrode proper, or 5, is shown in the form of a small member of shell formation, or cup, for example of nickel; the exterior bottom of the cup may be welded to the nickel o r other supporting wire 5b, winch in turn is welded to the leadin wire 4', so asto maintain the open top of the cup facing the center of the device I. On the bottom interior of the cup may, if desired, be welded the grating or mesh 5a (see Figure 4); the interior bottom of the cup, including the mesh 5a if employed, is coated with a suitable oxide or other coating according to well-known cathode coating practice. Supported about the electrode 5, coaxial therewith and spaced at least slightly therefrom, is an alumina or other ceramic tube 0a, of length preferably exceeding by several times the axial length of the electrode: preferably this will overhang the latter to a greater extent in the direction of the center of the device I than in the opposite direction. Surrounding the tube 6a. is a nickel or other metallic shielding cylinder 1, of appreciably greater diameter than the tube 6a -and preferably of slightly greater length; the cylinder 1 is maintained co-axial with the tube 0a by two mutually similar nickel or other metallic end-members 1a. and 1b at the ends respectively hole 1b', however, is desirably at least substantially closed. wherefore I may -provide the disc 3| secured against the outer face of the endmember 'Ib'within its peripheral flange. The

- electrode-supporting wire 5b may'pass through the disc 3I`within an'lnsulatlng bushing 3|.

A heater winding 6, preferably of relatively fine wire closely spaced, is provided about the tube 6a, for example for nearly the full length of the tube. Desirably there is coated and dried over the heater winding a solution of alumina powder in amyl acetate, or the like. to formr an insulating layer 6b in which the heater winding is imbedded; this reduces the danger of shorting of turns of the winding and otherwise renders the heater more sturdy. The extremities of the winding 6 are designated .as 32 and 34; the extremity 32 nearer the seal 2b is. connected to a refractory wire 33 which passes, through a refractory insulating tubing 33'.' outwardly of the chamber 30 formed between the tube 6d and the cylinder 'I, I

the wire 33 being welded to the lead-in wire 4' and thus electrically connected with the main electrode 5. The other winding extremity 34 is connected to the lead-in wire 4". which passes into the chamber 36 and longitudinally thereof into adjacency with the extremity 34; the leadin wire 4", from seal 2b substantially to its extremity, may be covered by a refractory insulating tubing 31. The third lead-in wire 4" may be welded to the cylinder 1, thus forming a connection to the entire enclosure I1a-'Ib, which in its entirety is designated as 'I'.

The external circuit illustrated in Figure 1 in association -with the device I may be simply described as follows: The lead-in wires 4' and |04' are connected to the line terminals 3 through ballasting means; these have been illustrated as the serially disposed choke coil Ila and incandescent lamp |617, though it will be understood that no limitation as to form of ballast is intended, and that either choke coil or lamp might be omitted. The lead-in wires 4" and |04" are connected together, placing the heater windings 6 and |08 mutually in series and together in parallel with the main discharge path between main electrodes 5 and |05. The lead-in wires 4" and |04" are. connected together through the resistor 40.

Thus the enclosures 'I' and |01' themselves form the auxiliary electrodes, and together with the resistor 40 from the starting circuit. Each enclosure, being in very close thermal association with the heater winding for the adjacent main electrode-or, in other words, forming a portion of the electrode heating fumace--is efficiently heated in denite relationship to the heating of that electrode; this relationship will of course be K somewhat different for different portions of the enclosure. In general, the portion of the enclosure principally active in performing the auxiliary electrode function will be that portion to which an emissive coatingfor example, similar to the main electrode coatingis applied, and I accordingly apply such a coating to that enclosure portion which heats in the most desirable relationship to the main electrode. While my incurrent actually flowing progressively decreasevention is not limited thereto, I have4 found such a desirable relationship in' general to be one wherein the enclosure portion heats somewhat more slowly than the main electrode proper; this preferred relationship will be further referred to hereinafter. The ,portion in question should also preferably be separated from the main electrode by a reasonably short and direct auxiliary discharge path. I have found generally satisfactory as an enclosure portiton to receive the emissive coating the outside surface 4| of the enclosure end-member la (and correspondingly the like surface |4| of the enclosure end-member |0111); coating of this surface has' been frictlonally illustrated as 4|s in Figure 3. I have alternatively successfully employed as a coated enclosure portion the interior surface 42 of the outward peripheral iiange of end-member 1a (and |42 of lola), and even the interior surface 43 of the inward central flange of the end member 'la (and |43 of |01a); and it is to be understood that in its broader aspects my invention is not limited as to the precise enclosure portion to receive the coating. An advantageof providing the effective auxiliary electrode on such a surface as 4|, which faces away from the adjacent main electrode and toward the center of the discharge device, is the favorable extending of the field of the auxiliary discharge in the direction of the center of the discharge device.

In order for the auxiliary discharge to take place across either of the auxiliary discharge paths, there must be available across that path a voltage slightly greater than the sum of the cathode fall (for small currents) and the ionization potential of the gaseous atmosphere in the path. As I ordinarily employ the system, the voltage available across each path is much less than the cathode fall with the electrodes cold; under these circumstances no discharge will take place when voltage is first applied across the system. But

' the cathode fall of each velectrode is rapidly lowered as a result of the progressive heating thereof by the winding 6 or |06. and in the course of several seconds will have fallen'to some valuepredetermined by the applied voltage, ionization potential, etcat which there occurs establishment across each auxillarvpath of a discharge, of which the current is at first negligible. 'I'he heating of the electrodes by the windings of course continues and the cathode fails for the to zero; then the drop across each auxiliary path may be only slightly greater than the gaseous ionization potential-for example, with an atmosphere includingv an appreciable amount of mercury vapor. the di op may be of the order of 15 volts.

'I'he function of the resistor l0 is. of course, the determination of a limiting auxiliary discharge rate (i. e., a maximum auxiliary discharge current), and hence a determination of the steepness of rise of the auxiliary discharge current. This current at any instant during the auxiliary discharge is given by the value of the resistor 40 divided into thevoltage across it; the latter is substantially the line voltage less the then existent `ballast drop, less the then existent cathode fall (times two) and less the gaseous ionization potential (times two). Thus when the electrodes have reached ,substantially zero fall for the current then flowing (assuming at the moment a 20 volt drop in the ballasting means. allowing 15 volts for drop in each auxiliary discharge. path, and assuming 120 volts applied across the system), some '70 volts will then be impressed across the resistor 4|), and the auxiliary disch-arge current will be this '70 divided by the resistance duction of ions and (since the ions it producesl .are subject to some steady losses) the rate of its production of ions; this critical value is sufficient to have materially cleared away electronic wall charges and'otherwise to permit the striking of the maindischarge between the main electrodes. and at such instant the main discharge will strike. If the value of resistor 40 be made relatively low, and the auxiliary discharge;- current at given instants (and thus its steepness of rise) therefore relatively high, rthis critical ionizing value may be reached too soon bythe auxiliary discharge. Thus, for example, it might be reached even before the main electrodes had been heated to a temperature sufficient to eliminate their cathode fall as to the auxiliary discharge current (which willbe understood in turn to be a lower temperature than that required for elimination of cathode fall as to the and their coatings. l Again, critical ionizing value might be reached by the auxiliary discharge after the mainelectrodes had been heated to a temperature sufficient to eliminate their cathode .fall as to auxiliary dischargel current. but still insufllcient to eliminate cathode fall aste the main discharge current value; this condition would be an improved one, but the main discharge starting would still be premature. Of course, if the value of resistor 40 be made too high, critical ionizing value may never be reached by the auxiliary discharge, in view of the signicance, as to that value, or rate of ion production.

I prefer so as to adjust the value of resistor 4|) that the auxiliary discharge reaches critical ionizing value substantially at the time the main electrodes have just reached the temperature of negligible cathode fall as to the main discharge current value. Since rate of the auxiliary discharge may be an important factor in the establishment of critical ionizing value, it is desirabler changing. But it is to be noted that after the main electrodes have reached that relatively lower temperature which is sufficient to eliminate their cathode fall as to the auxiliary discharge, the influence of'their' temperture on the rate of the'auxiliary-discharge is at an end. -I accordingly prefer to make the auxiliary electrodes the essential determinants of the rate of the auxiliary discharge, and to make them the sole such determinants during the latter portion of this discharge; thus at the time when critical ionizing value shall have been reached by the auxiliary discharge, although the` main electrodes should already have ceased to be of influence on that discharge, the. auxiliary electrodes desirably` still have, or havejust stopped having. a cathode fall. This is caused to occur by the sov occur (in similar directions relative to the positive column path) in both its paths during each one half cycle. 'I'his has the effect of minimizing l the maximum instantaneous rate required of the auxiliary discharge for the reaching of critical ionizing value. From a converse point of view, with reasonable and readily attainable maximum rates of auxiliary discharge I am able to start relatively long and/or narrow and/or specially shaped devices. And this fact, in conjunction with the elimination of reliance on any momentarily high voltage or surge, makes entirely successful the operation of devices and systems of the extremely simple -type shown and described or. supply voltages of as low a`s 100 volts peak-which obviously more than meets the requirement for operation on normal commercial lines rated at or near 110 volts R. M. S.

As soon as the main discharge has struck thereof course occurs a signicant redistribution of voltages in the system; this results from the establishment across the device I of a voltage materially lower than the line voltage minus auxiliary discharge current drop in the ballasting means. since a much higher current now ilows through the ballasting means. Typically in a system with the parameters abovementioned the voltage across the device may be oi the order of 35 volts. and the normal or main discharge current through the ballasting means of the order of 2 amperes. A discharge still tends to occur in each auxiliary discharge path,with a voltage drop in each of a value lying in typical cases in the range from av few volts toaround gaseous ionization potential-typically some 5 to l0 volts, But in view of the now low voltage across the device, the voltage .remaining to drop across the resistor 40 will be low. and hence the current through the' each auxiliary discharge path, or the current through the auxiliary discharge circuit as an entirety, will be small. This, of course, automatically obviates any serious powerv loss in that circuit during main discharge continuance.

a 'Ihe material reduction lof voltage across the device by the main discharge is employed to an other even more fundamental advantage in the system which I have illustrated. This is the *accompanying reduction of current through the heaters and |00, automatically maintaining at a reduced value their heating eifect on the main electrodes throughout the time' while the main discharge is contributing to the heating of those electrodes; thus dangers oi overheating the electrodes are greatly minimized, while fast initial heating is nevertheless achieved. 'I'his desirable action is produced by shunting of the heaters or heater circuit directly around the main discharge path, or around the device proper, rather than across. the entire system or across the supply voltage or some voltage always proportional thereto. Since the period of the auxiliary discharge is relatively short, the heaters may then be permitted to receive substantially more current than they could carry continuously, being designed essentially as elements eiiiciently opera-v tive at their relatively low normal operation voltage-and this with the assurance that this normalvvoltage willv be very exactly maintained ionization potential.

throughout normal operation, in spite of wide line voltage fluctuations. 'I'his assurance of normal operating voltage constancy I have round very beneilcialin the construction of relatively highvoltage but fast-acting and long-lived heater windings.

An incident of the disclosed arrangement of the heater windings-mutually in series and together in parallel with the main discharge pathis of course the impression across each of a voltage exceeding the ionization potential of the gaseous atmosphere within the envelope. Under such circumstances, and in the absence of appropriate preventives there exists serious danger of arcbacks, particularly between different portions of the same heater, as well as materially increased danger of the main discharge occurring to some portion of the heater system in either end of the quent cases jointly necessary to provide assurance' from destructive arcing effects. One of these is the extension of the enclosure, or shielding, about at least that heater lead-in wire (c. g., 4) which is at a potential different from the respective main electrode potential by more than the gaseous may be desirable to extend the shielding also about the connection from the opposite heater extremity, in such a system as illustrated in Figure 1 this is unnecessary since this connectionwire 33-is at main electrode potential.

The other specification to which I have above made reference is especially intended to prevent any minute or incidental arcs from forming; for the formation of any form of arc wipes out, at the spot or spots of the arc occurrence. the normally high cathode fall of the heater (resulting from its material, for example tungsten, and lack of oxide coating), which is a factor on which reliance is necessarily placed in arc-back prevention. This speclilcation is that in spite of its completeness the enclosure be arranged so that its -inner surface always maintains a materially lower temperature than the surface which by a sufilcient spacing of enclosure from heater.v

The reason for its importance appears to be as follows: 'Ihe winding 8 is subject to 4some steady disintegration; this takes place into the space within the enclosure whether or not the relatively porous coating layer 6b be-employed. y The While in certain cases'it disintegrated material, which is of coursemetallic, deposits or condenses on thegrelatively coolest nearby surface; if the surface carrying the winding is permitted to be cooler than or even of the order of coolness of `the interior enclosure surface, a very significant metallic deposit will accumulate thereon. 'I'his leads rapidly to the development of heater-shorting currents which,

as they develop and/or as they burn out the thin deposit in spots, produce minute arcs. These,

for the reasons abovementioned, render the winding very prone to the formation'of arc-backs, especially between different Winding spots. (Also the partial shorting of the heater raises the current' in the balance to abnormally high values, reducing cathode fall and in that manner facilitates the production of arc-backs.) But by maintaining the enclosure 1', particularly its surface disposed toward the heater, materially cooler than the surface which carries the heater winding, the deposit is caused to form almost wholly on that enclosure surface, where it does no damage.

It will be understood that while the preferred circuit according to my invention is that illustrated in Figure l and above described, I may employ the 'relative arrangements of main and auxiliary electrodes, and of each of these with the heating means, in other circuits. Thus in Figure 2 I show the device I of Figure 1 with an external circuit-in itself known as a ystarting circuitfrom which the resistor 40 is omitted and replaced by two resistors 50 and 5|; these are respectively connected from the lead-in wire 4" (for the auxiliary electrode 1') to the leadin wire |04' (for the cathode |05), and from the lead-in wire |04" (for the auxiliary electrode |01') to the lead-in wire 4' (for cathode 5). 'Ihe auxiliary discharge now of course takesplace in two parallel, rather than serially disposed paths-but, in spite of alternating current operation, it again occurs in similar directions in both its paths during each half cycle. Of course only one cathode fall is to be accounted for in each path; this being borne in mind, the resistorsS and 5| may be apportioned according to the -general principles above set forth for the resistor 40.

Still another circuit embodying the disclosedl nected to a point on the respective heater-as by welding to the enclosure of a tap 38 or |38 from the respective heater. Thus each auxiliary discharge path becomes a shunt, connected internally of the device around at least a portion of the respective heater (this portion being designated as 6s or |06s), and only two lead-in wires (4' or |04' for cathode and 4" or |04 for heater extremity) `need issue from the device at each extremity thereof,

The external circuit comprises the connection, as before, of lead-in wires 4 and |64 to the line terminals 9 through the ballast means (e. g., |6a,|6b); and the connection of leads 4" and |04" together, optionally through an impedance such1as the resistor 40a. As to the enclosures or auxiliary electrodes, this resistor together with the unshunted heater portion is obviously connected similarly to the resistor 40 of Figure l. The operation, however,v is vsomewhat distinct from that of Figure 1; for in that vfigure no voltage drop occurred in the resistor 40 excepting heater portions.

current as well flows through and produces a order of resistance value than is the resistor '40 of Figure 1. It is to be-noted .that this heater current drop obtains as soon as voltage is applied across the system,'so that the potential diierence between each auxiliary electrode and the respective main electrode is initially not as high as in the lcircuit of Figure 1. Since no discharge can initiate' until the cathode fall has been reduced (as a result of electrode heating by the winding 6 or |06) to' at least as low as the peak value of this potential difference, the starting of any discharge with the circuit of Figure' tends to be longer delayed from the vinstant of first applying voltage across the system; as the cathode falls progressively reduce, however, a discharge will start, executing a materially more f rapid rise of rate (i. e., of discharge current) than in the case of Figure 1 in view of the mentioned vlower order of resistance value. When this auxiliary discharge has reached critical ionizing value, the main discharge will lstrike as in` the case of the systems of earlier figures. .Also

as in those systems. the main discharge will materially lower the voltage'drop across the device` As in those cases, I prefer in this casev so to adjust the parameters that critical ionizing value .f

will be reached by the auxiliary discharge approximately as the main electrodes reach normal operating temperature and hence emissivity. In

those cases I performed such adjustment by freel ly regulating the value of the seriesresistor or resistors to infiuencethe limiting auxiliary discharge rate and steepness of its rise. In this case, however, the limiting 'auxiliary discharge rate and steepness of rise being. inherently high,

I rather perform the adjustment by regulating 'f the voltage initially dropping across each auxillary path, thereby infiuencing the interval of delay before auxiliary discharge initiation-an interval during which the electrodes are of course llaisng progressively heated by the windings 6 and It win be understood that, in view `of the use of resistor 40a, it is possible to place the taps 38 and |38 if desired at or near the respective heater extremities 34 and |34, thus either completely l or substantially eliminating any unshunted Conversely, when substantial unshunted heater portions are employed, it is possible to omit (i. e., by short-circuiting) the resistor 40a. In the usual instance of employment of the circuit of Figure 3, I have preferred so to'omit'the resistor 40a, in ordei` to avoid the inherent power loss therein. In typical' such cases I have placed the taps 38 and I|38 at points across each unshunted portion a voltage 0f about 33 volts. When the auxiliarydischarge develops and, increases these respective voltages would shift to the order of I0 and 35 the system voltage having dropped in the order of l0 volts due to increased ballast drop. When the main discharge strikes these respective voltages would shift to the order of 5 and 121/2 volts-the system voltage having dropped to some 35 volts due to now high ballast drop.

The connection of the auxiliary electrodes 'I' and |01' into the heater circuit in Figure 5 has so far been considered in connection with influence on the auxiliary discharge; there are however, converse inuences on the heater circuit and on its electrode-heating functions. During the 4time vinterval through which the auxiliary discharge is taking place, this discharge, in view of the reducing cathode fall, is progressively lowering the voltage across the shunted heater portions 6s and I06s, and hence the current therethrough; finally, during the continuance of the main discharge, the voltage across each shunted heater portion is maintained 'at less than the gaseous ionization potential. If the resistance values in the entire heater circuit are so arranged thatinitially there drops across each shunted heater portion 6s and IlJBs a considerably higher voltage than this nal one, the above-mentioned progressive lowering of heating eil'ectof these portions will be very appreciable. To secure a corresponding thermal effect on the electrodes, however, the unshunted heater portions are preferably maintained small or eliminated (an appropriate value of external resistor 40a being employed). This is because, as the current in the shunted heater portions is progressively reducing, the current in the unshunted heater portions is tending progressively to increase and counteract the former in effect on the electrodes. Theaction discussed in this paragraphtaking place during the progress of the auxiliary discharge-is of course not to be confused with that reduction which results from sudden great lowering of the voltage across the entire heating circuit upon striking of the main discharge. The action described in this paragraph is therefore most advantageous when, because of small ballast or other special factors.

the degree of voltage reduction upon main discharge striking is not high.

Another inuenceon the heater circuit of connection of the auxiliary electrodes into that circuit is the establishment of a strong tendency to equalization of temperature and emissivity of corresponding electrodes in the two ends of the device. While theoretically equality between such electrodes would always exist as a result of symmetry of arrangement, in practice there frequently tend to be some inequalities which the effect now under discussion greatly minimizes. Thus for example let it be assumed that as a result of discrepantelectrodes temperatures the auxiliary discharge is occurring with a given drop in a rst vof the paths, while in the second opposite path the discharge either is occurring with a higher drop or has not yet started; it is then obvious that greater voltage and current appear across and pass through the second heater, speeding up the heating of the electrodes associated therewith. This equalizing tendency will be understood to continue throughout the duration of the auxiliary discharge in both paths; thus the arrival of the twomain electrodes at normal high temperature is synchronized, and possibilities are precluded of one main electrode heating extra rapidly and causing the auxiliary discharge to reach critical ionizing value before the other main electrode is properly heated.

While in the electrode structures 4a and IMa there may be employed a main electrode 5 identical with that of earlier figures, I have illustrated in the structure la of Figure 5a a main electrode 95 of alternative form. This comprises a nickel cup 96 which. while permissibly of solid material. is desirably of fine mesh. This cup is filled with a mixture 91 of alkaline cathode coating material (such as barium and strontium voxides or 5 carbonates) with flake nickel, permissibly in an organic carrier such as amyl acetate; the size of the flakes for example has beenof the order of 11g" by `1*, x .00004". This mixture has been packed into the cup 98, and the filled cup baked l at high temperature in a hydrogen atmosphere to remove the carrier, at least partially to de-gas the electrode, and to produce alkaline oxides from the carbonates if the latter have been employed. The electrode 95 has then been as-l sembled into the electrode structureand device in the same manner as the electrode of prior figures. This main'electrode 95 remains one of very small mass, well adapted to function in the "furnace" type of electrode structure illustrated herein and to heat with the desirable greater rapidity than the coated enclosure portions forming the auxiliary electrodes.

While the devices and systems which I have above disclosed are nicely adapted for operation from alternating current, it will be understood that they may be employed for operation from direct current (choke coil ballast IBa being of course omitted). It is further to be understood that at least most of the features of utility remain of value in such direct current operation. Thus for example, although the desirable formation of auxiliary discharges in both ends of the device does not, with any particular connection to direct current, require the efficiently provided emissivity of both auxiliary electrodes, it insures the existence of that emissivity of the appropriate one of those electrodes when the system is connected without regard to polarity. It

is also to be understoodthat certain of the advantages of particular features of my invention will be retained, with either alternating or direct current, even though one of the auxiliary electrodes be omitted and an auxiliary discharge therefore employed in one end only of the device.

It will finally be understood that while I have disclosed my invention in terms of particular embodiments thereof, I do not thereby intend any unnecessary limitation; rather I undertake to claim my invention as broadly as the state of the .504

art will permit. There is made, however, no claim in this application specific to the embodiment of Figures 5-5a-that is, no claim readable thereon and not readable on other of the embodiments-such claims having been made in sive electrodes a substantial auxiliary discharge prior to and for starting said main discharge, comprising heating means serially connected in said circuit and including a single heater disposed in suilcient heat-transferring relation to both said thermally emissive electrodes to heat both of them to a temperature of appreciable free thermionic emission.

.2. In a gaseous discharge system for alternating current operation having a discharge path, means for maintaining a main arc discharge therein, an electrode-heating circuit, and means for passing through said circuit a heating current which attains its full value prior to the inception'of said main discharge: the combination of a thermally emissive main electrode forming a terminal of said path; a thermally emissive auxiliary electrode near said main electrode; and means for causing between said thermally emissive electrodesv a substantial alternatingly bidirectional auxiliary discharge prior to and for starting said main discharge, comprising heating means serially connected in said .circuit and disposed in suiiicient heat-transferring relation to said thermally emissive electrodes to heat both of them to a temperature of appreciable free thermionic emission.

3. In a gaseous discharge system including two main cathodic electrodes and means for causing a main arc therebetween: means for starting said arc comprising two thermally emissive and serially connected auxiliary electrodes respectively near said main electrodes and forming therewith serial auxiliary discharge paths, means for impressing between said main electrodes a voltage insufficient to establish substantial discharges in said paths when the auxiliary electrodes are cold, andmeans for bodily heating said auxiliary electrodes suillciently for the establishment of such discharges.

4. In a gaseous discharge system including two main cathodic electrodes at mutually diierent potentials: means for starting a main arc between said electrodes comprising two thermally emissive auxiliary electrodes respectively near said main` electrodes,` each 'auxiliary electrode having at any instant a potential relative to its respective main electrode of polarity similar to that of the opposite main electrode and of magtem: means for causing a main arc discharge, in-

cluding a main electrode adapted for cathodic action; means for causing an auxiliary discharge, including an auxiliary electrode near said main electrode; and heating means adjacent `said electrodes for lowering the cathode fall of each, said iirst mentioned means being responsive to a critical value of said auxiliary discharge, and said second mentioned means being responsive to said electrode cathode fall lowering.

6. In 'combination in a gaseous discharge system: means for supporting a main arc discharge including a thermally emissive main electrode adapted for cathodic action; an auxiliary elec-V trode near said main electrode; means for initially heating both of said electrodes; and means for causing said main discharge to strike, said means being at least principally responsive to auxiliary electrode temperature.

7. In combination in a gaseous discharge system: means for causing a normal main arc discharge, including a main electrode adapted for cathodic action; means for causing an auxiliary discharge, including a thermally emissive aux- `iliary electrode near said main electrode, and including means for establishing a maximum auxiliary discharge rate; and heating means adjacent each of said electrodes for eliminating the cathode fall lof said auxiliary electrode as to said maximum auxiliary ,discharge rate, and for at least substantially as quickly eliminating the cathode fall of said main electrodeas to the rate of said normal main arc discharge.

8. The method of starting a main arc discharge between two main electrodes which includes forming, along distinct portions of the main discharge path, two simultaneous auxiliary arcs each of small cathode fall and instantaneously similarly directed along said path.l

9. The method of starting a main arc discharge between two main electrodes which includes forming, along respective terminal portions of the main discharge path, two simultaneous auxiliary arcs each of small cathode fall and instantaneously similarly directed along said path.

10. The method of starting a main arc between cathodic main electrodes, which comprises impressing, across auxiliary discharge paths formed betwe said electrodes and respective adjacent auxili ry electrodes, alternating voltages phased for the establishment of simultaneous auxiliary discharges in similar directions as viewed along the main discharge path but insufcient for the establishment of substantial discharges to the auxiliary electrodes as cathodes when the auxiliary electrodes are cold, and

the auxiliary electrodes.

1'1.` In combination in a gaseous discharge system: a main discharge supporting electrode; a heating furnace for and surrounding said main electrode; and an auxiliary electrode and means for causing an auxiliary discharge betweenthe same and said main electrode, said auxiliary electrode being a portion of said furnace.

l2. In combination in a gaseous discharge system: a main discharge supporting electrode: a heater winding in heating relationship to said main electrode; an auxiliary electrode and means for causing an auxiliary discharge between the same and said main electrode; and an enclosure for said winding in substantial heat-responsive relation thereto, said enclosure comprising said auxiliary electrode.

13. In combination ina gaseous discharge system: a main discharge supporting electrode; a heater winding in heating relationship to said main electrode; an auxiliary electrode and means for causing an auxiliary discharge ybetween the same and said main electrode; and an enclosure for said winding in substantial heat-responsive relation thereto, said enclosure carrying an emissive coating and comprising .said auxiliary electrode.

14. In combination in a gaseous discharge device: a main discharge-supporting electrode; a heating furnace for .and surrounding said electrode; andan auxiliary electrode comprising an emissive coating on a portion of theexterior surface of said furnace.

15. In combination in a gaseous discharge device: main electrodes, an auxiliary electrode between said main electrodes and adjacent one of them, and an emissive coating carried by said auxiliary electrode only on a surface thereof facing' away from the adjacent said main electrode.

16. In combination in a gaseous discharge de- `establishing such discharges by bodily heating vice: main-electrodes, an auxiliary electrode bevice: an electrode; a heating surrounding said electrode; a shield surrounding said' winding; and an end member for said shield,

centrally apertured to expose said electrode. and

carrying an emissive coating.

RICHARD M. SOMERS. 

